In autoimmune hemolytic anemia (AIHA) associated with Mycoplasma pneumoniae infection, the responsible antibodies are:

• A IgG warm antibodies against Rh antigens
• B IgG antibodies against DAF (CD55) causing complement lysis
• C Donath-Landsteiner antibodies (IgG) against P antigen
• D IgM cold agglutinins reacting with RBC I antigen at temperatures below 37°C ✓

Explanation

Cold agglutinin disease following Mycoplasma pneumoniae infection (and also infectious mononucleosis) is caused by IgM antibodies that agglutinate RBCs optimally at 0-4°C by binding to the I antigen on the RBC surface. At warmer temperatures they dissociate, but complement C3b remains, leading to extravascular or intravascular hemolysis. Warm AIHA uses IgG. Donath-Landsteiner antibodies (anti-P) cause paroxysmal cold hemoglobinuria. CD55 loss is PNH.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.